The forming of small diameter rounds from larger bars is known in the milling art. Generally, a large bar is successively passed through a series of rollers that reduce the cross sectional area of the bar and, through a number of intermediate steps, eventually forms the desired shape. In this context, the bar includes not only a bar whose cross section is substantially round, but also a bar whose cross section is slightly oval or square-shaped and a ribbed bar which is the above-mentioned bar, on which ribs are formed. Because the amount of the reduction of the cross sectional area on each pass through the rollers is limited, the smaller the cross sectional area of final product, the larger the number of roller passes, machinery and production floor space required.
The simultaneous forming of multiple rounds significantly reduces the above-stated problems because the reduction in total cross sectional area is considerably less, therefore, fewer intermediate steps are required and the speed and length of the end product is reduced.
It is known in the art to simultaneously produce two uniform metal rounds and three uniform metal rounds. The simultaneous production of three rounds is described in U.S. Pat. No. 4,357,819.
In addition, the following methods for producing a plurality of bars from a single preformed billet in a finishing rolling train have also been proposed:
(1) A method for simultaneously producing three strands of bars from a single preformed billet in a finishing rolling train, is disclosed in Japanese Patent Application Laid Open No. 24,503/84 of Feb. 8, 1984 (hereinafter referred to as the "Prior Art 1). PA1 (2) A method for simultaneously producing four strands of bars from a single preformed billet is disclosed in Japanese Patent Application No. 92,001/85 of May 23, 1985 (hereinafter referred to as the "Prior Art 2").
In this method, a finishing rolling train is composed of 4 stands K.sub.4, K.sub.3, K.sub.2, and K.sub.1 (not shown) arranged in series in the rolling direction. The K.sub.4 and K.sub.3 stands roll a preformed billet to produce three strands of bars 2a, 2b and 2c connected to each other by means of thin connecting portions 2d and 2e as shown in FIG. 9(A). A pair of slit rolls (not shown) cut the three strands of bars 2a, 2b and 2c along the connecting portions, and then stand K.sub.2, composed of a pair of calibered rolls, rolls the three cut strands of bars 2a, 2b and 2c to produce bars of oval cross section as shown in FIG. 9(B). Then stand K.sub.1 composed of a pair of rolls with a finishing caliber (a bore type), rolls the three strands to produce final product bars 3a, 3b, and 3c as shown in FIG. 9(C). FIG. 9(A) shows a state of rolling a billet at the stand K.sub.3. FIG. 9(B) shows a state of strands having been cut off by means of a pair of slit rolls, following the K.sub.2 stand. FIG. 9(C) shows the shapes of bars 3a, 3b and 3c after the bars have been rolled at the stand K.sub.1.
The "Prior Art 2" was developed to enhance the productivity of the method of the "Prior Art 1." According to the method of the "Prior Art 2,"bars are produced as follows:
Four strands 4a, 4b, 4c and 4d connected to each other by thin connecting portions 4e, 4f and 4g are formed as shown in FIG. 10(A) by means of stands K.sub.4 arid K.sub.3 (not shown). The four strands 4a, 4b, 4c and 4d as shown in FIG. 10(B) are cut off along the central connection portion 4f by means of a first pair of slit rolls (6) between stands K.sub.3 and K.sub.2 (not shown) as shown in FIG. 11. Then, four bars 4a, 4b, 4c and 4d as shown in FIG. 10(C) are obtained by cutting off along the connecting portions (4e, 4g) by means of two pairs of second slit rolls (7, 8). Subsequently, bars 5a, 5b, 5c and 5d as final products, as shown in FIG. 10(D), are produced by simultaneously rolling the four bars 4a, 4b, 4c and 4d. Processes of rolling and cutting the strands are shown in FIGS. 10(A) to 10(D) and the positions of the slit rolls on the plane are shown in FIG. 11.
As compared with the simultaneous production of three rounds, the additional problems involved in producing four rounds simultaneously from one bar are significant. The problems include maintaining the uniformity of the cross sectional areas of the strands as well as avoiding the cobbling of the strands during the slitting process. Other considerations include the resistance produced when separating the strands, which resistance can result in excessive heat, lower separating speeds and lower efficiency.
The preferred embodiment of the method and apparatus of the present invention includes simultaneously slitting a billet into more than four strands or rounds by forming the billet into the desired number of shapes for rounds and separating the outer most strands from the remaining billet before separating the next outer most set of strands from the billet until the billet has been divided into a desired number of strands. Where there is an odd number of strands to be separated, of course, when the last pair of outer strands is separated only the inner most or center strand will remain.